1. Field of the invention
The present invention relates to a hydraulic vibration buffer.
2. Description of the Prior Art
A helicopter is one example of a moving body which is subject to substantial vibrations. The rotating portions such as the engine etc. cause the body as a whole to vibrate, but it is preferred that vibration of seats, measuring instruments, etc. be minimized.
To this end, various vibration dampers and shock absorbers have been proposed. For example, such a device is shown in FIG. 2. In this device a case 52 is attached to seat 51 or the like, and a displaceable main weight 55 is housed in the case 52 and elastically supported by springs 53 and 54 extending from opposite sides as shown. An adjustment weight 56 is swingably coupled with the main weight 55. An actuator 57 attached to the case 52, is coupled by a link mechanism 58 to adjustment weight 56. A speed sensor 59 is provided for detecting the speed of displacement of the main weight 55, and an acceleration sensor 60 for detecting the acceleration of vibration of the case 52. Control means 61 controls actuator 57 on the basis of the respective outputs of the speed and acceleration sensors 59 and 60.
In this device, the actuator 57 is actuated responsive to the speed and acceleration sensors 59 and 60 so as to automatically adjust the position of swing of adjustment weight 56, that is, the position of center of gravity of the adjustment weight 56, and consequently the frequency of vibration of the seat 51 is made to accord with the natural frequency of the whole of the main weight 55 and the adjustment weight 56, so that the vibration energy of the seat 51 is absorbed by the main weight 55 and the adjustment weight 56.
In such a device, however, there has been a problem that, since vibration is absorbed by the main and adjustment weights 55 and 56, each having a large inertia mass, the response rate to the change of the frequency of the vibration source (that is, the seat 51) is so low that the effect of vibration absorption is extremely low at transient times. Moreover, there has been another problem in that the device as a whole is large in size and heavy in weight and the device is low in reliability because of use of an electric circuit and various sensors.